Sprinklers utilizing a fixed nozzle to emit a stream onto the grooves of a viscously damped rotor plate are known in the art and examples of such constructions may be found in commonly owned U.S. Pat. Nos. 5,288,022 and 5,058,806. Sprinklers of this type may be incorporated into pop-up type arrangements or they may be mounted on, for example, fixed riser pipes. In either case, it is possible to employ adjustable or interchangeable nozzles having orifices which emit a 360° stream, a 180° stream, a 90° stream, etc. so as to produce a desired sprinkling pattern, to be determined primarily by the location of the sprinkler. There is also a need, however, to be able to adjust the throw radius and flow rate of the sprinkler without varying the water pressure.